The present invention relates to a pressure monitoring system, and, more particularly, concerns such a system for use with an electrofluidic device for sensing pressure, such as devices for monitoring intracranial pressure within the skull of a patient, and the like devices.
The accumulation of data relating to pressure measurements of various areas of a patient before, during and after surgery is heavily relied upon in order to provide a satisfactory understanding of the patient's tendencies. For example, the monitoring of intracranial pressure in patients who have undergone neurosurgery or who have hydrocephalic conditions provides the medical staff with information on the trends of pressure levels and serves as a clear indication should the intracranial pressure rise to levels which could cause brain damage or worse. One technique for monitoring pressure which is particularly amenable to procedures of intracranial pressure monitoring includes the employment of a device known as a Numoto switch. The Numoto switch is a pressure-actuated device generally constructed of a thin, flat flexible envelope, and a pair of electrodes inside the envelope usually attached to the flat walls of the envelope and movable so that, depending upon the pressure inside the envelope, they may either contact each other or move away from each other. An electrical lead is connected to each electrode to provide an electrical connection therefor. A flexible air tube is generally connected to the envelope both for providing air, or other fluids, into the envelope and for enclosing the electrical leads which extend therethrough. By an appropriate connection, the Numoto switch is connected to a fluid source for providing fluid into the envelope and also for indicating the pressure level of the supplied fluid.
This Numoto-type switch and one application and technique of using the same is described in U.S. Pat. No. 3,649,948. In the procedure explained in this patent, the switch is implanted within the skull of the patient in order to be in proper position for detecting intracranial pressure. As long as this intracranial pressure applied to the envelope of the switch exceeds the air pressure within the switch, the two electrodes will be maintained in contact with each other, serving as a closed electrical switch. Through the electrical leads, this switch is indicated on an ohmmeter as being closed; this then alerts the operator that the applied intracranial pressure exceeds the pressure inside the switch envelope. To detect this applied pressure level, the operator, relying upon fluid inside a reservoir of a manometer, slowly injects the fluid through the flexible tubing into the switch envelope. When the pressure inside the envelope just exceeds the intracranial pressure, the walls of the envelope are forced apart, whereupon the electrodes separate, and electrical contact is broken. Once again, through the electrical leads, the ohmmeter provides an indication that electrical contact has been broken inasmuch as the ohmmeter indicator should now read zero. At this point, the operator reads the pressure level of the injected fluid on the manometer. The balance of applied pressure and fluid inside the envelope is maintained by the operator alternately withdrawing and injecting fluid from the reservoir into the envelope, causing the electrical contacts to close and open with this alternating procedure.
It can be seen that utilization of the Numoto switch for monitoring pressure, and particularly intracranial pressure, is a reliable device inasmuch as only the straightforward balance of internal pressure inside the switch envelope with applied external pressure is required. However, the fluid providing system, the electrical monitoring approach and the pressure level reading element of the total system described in U.S. Pat. No. 3,649,948, while apparently workable in many respects, is deficient in others. Particularly, the fluid injection system to alternately balance the internal pressure with the applied external pressure is apparently performed manually by the operator; this, of course, is cumbersome for many applications of this type switch, and needs an operator for its performance. In addition, the operator must first observe the detection needle on the ohmmeter in order to have knowledge when the electrodes are either in contact or out of contact with each other, while at the same time trying to observe the manometer for the pressure level reading. Moreover, the manometer is merely a pressure gauge which oftentimes does not provide the accuracy which is necessary in situations such as the monitoring of intracranial pressure levels.
With these deficiencies in mind, it can be seen that there is room for improvement in many aspects of a pressure monitoring system which particularly uses an electrofluidic pressure sensing device, such as the Numoto switch. In particular, more reliance on automation is desirable inasmuch as this would substantially reduce the operator's time and attention for the mechanical aspects of operating such a system. Furthermore, clear, accurate readings, preferably digitalized, would provide a significant aid to the medical staff in assessing the pressure level readings. Various safety features, including an effective alarm system, are also desirable to provide an indication when dangerously high levels of pressure are being encountered; these safety features would also desirably be activated automatically so that constant attention to the display meter would be unnecessary. Other areas of improvement may also be incorporated in a pressure monitoring system of this device as desired by the operator.